A derailleur bicycle usually comprises a rear derailleur mounted in association with the rear wheel of the bicycle. Besides the rear derailleur system, there is a front derailleur mounted to the seat tube of the bicycle frame and associated with the chain wheels that is fixed to and thus rotatable with the pedals of the bicycle. Usually, each of the derailleurs is controlled by a manual shifter which is mounted on the handlebar or the down tube of the bicycle at a location ready to be operated by a bicyclist sitting on the bicycle saddle. The movements of the manual shifters are independently transmitted to the derailleurs by means of cables connected therebetween to switch the drive chain of the bicycle between chain wheels of different diameters at the front and rear chain wheel sets.
Conventionally, the front derailleur system is down-pull type which means that the cable that controls the front derailleur has to extend to surround around the bottom of the bicycle frame and then upward to the shifter. An example of the conventional down-pull type front derailleur is shown in FIG. 3 of the attached drawings.
In FIG. 3, a portion of a bicycle frame 90 to which the conventional front derailleur 94 is mounted is shown. The bicycle frame 90, as is well known, comprises a seat tube 93 and a down tube 95, both being jointed to a five-pass joint member on which the pedal is rotatably mounted. The five-pass joint is invisible in FIG. 3. The front derailleur 94 is secured to the seat tube 93. The front derailleur 94 comprises a moving block 940 pivoted thereto and a chain mover member 941 which is pivoted to the moving block 940. The chain mover member 941 has an opening or slot through which the drive chain 92 which is drivingly engageable with one of the chain wheel sections of the front chain wheel set 91 extends.
The front derailleur 94 comprises a cable 942 which has one end secured to the moving block.940 and an opposite end extending downward to partially surround around the bottom of the frame 90 and then upward along the down tube 95 to be secured to the manual shifter (not shown in FIG. 3) so that by operating the shifter by the bicyclist who is sitting on the saddle (not shown), the cable 942 pulls the moving block 940 downward to move the chain mover member 92 to switch the drive chain 92 between the chain wheel sections of the chain wheel set 91.
Since the front derailleur 94 and the connection thereof with the cable 942 are completely un-shielded, once the bicycle moves through muddy surface or is used in a bad weather, wet dirt in the form of mud or paste may attach to the moving parts of the front derailleur 94. When the dirt dries, it may become solid and hard and thus interfere the pulling of the cable 942 and the operation of the front derailleur 94.
It is therefore desirable to provide a bicycle front derailleur structure which overcomes the above-mentioned problems of the conventional, down-pull type bicycle front derailleur.